1. Field of the Invention
The invention relates to a wheel rut-resistant carriageway as well as to a process for obtaining such a carriageway.
2. Description of Background and Relevant Information
A carriageway comprises generally a foundation layer, a base layer, a binding layer and an upper layer. All these layers consist of materials treated with either hydraulic or tar binders. The materials and the binders are determined in relation to the type of traffic that the carriageway has to sustain or, in other words, in relation to the type of wear and deformation to which the carriageway will be subjected when in use. One of these phenomena to which the carriageway is thus exposed, is the formation of wheel ruts.
The ruts, generally defined as deep tracks or marks left by the wheels of a vehicle on a path, result from the load of the vehicles circulating over the carriageway and from the temperature rise of the said carriageway.
Indeed, the formation of wheel ruts in a carriageway comprising bituminous concrete layers is boosted when the temperature of the carriageway or of one of the layers, exceeds the softening temperature of the bitumen of the layer. The carriageway temperature results mainly from the ground temperature on which the carriageway lies and from its exposure to the sun. Moreover, a carriageway designed to sustain the traffic of heavy vehicles undergoes greater stresses in areas such as an approach to a highway toll where the carriageway must sustain the braking of the vehicles or the storage of the trucks in the waiting queues than in the driving zones of the highway lanes.
To remedy this particular fragility of the carriageways, it may be contemplated to build the highly stressed zones of the latter essentially as concrete slabs. However, this solution is solely retained for the new construction of zones of this nature since, in such a case, the time required by concrete to set is acceptable. On the other hand, when repairing the carriageway, this time for the concrete to set is too long and implies traffic prohibitions for trucks for an unacceptable duration.
Wheel ruts in carriageways are dangerous since they channel rainwater and make the carriageway slippery; the more so for trucks when they have to brake when approaching zones such as toll stations. Various technologies have been used to avoid the formation of wheel ruts. Thus, a method consists in mixing the bituminous binder with a mixed load of mineral granulates and waste flakes of plastic material (FR-2.742.174). Another technique consists in using a road coating compound comprising a tar concrete and acrylonitrile fibres, preferably kidney-shaped ones (FR-2.647.822).
Besides, tests have been conducted with `white` coated materials to benefit from the fact that this color absorbs heat less than the usual black tone of bitumen. However, the resistance of such coated materials to the formation of wheel ruts is very poor.
The various techniques described hereabove can be summarized as some kind of replacement technique: part of the agregate is replaced by voids, these voids being obtained by an appropriate choice of the particulate grade of the agregate.
Whatever the resistance to the formation of wheel ruts in the bituminous layers prepared according to these various techniques, none of the latter gives complete satisfaction.